func isAnagram(s string, t string) bool {
    if len(s) != len(t) || s == t {
        return false
    }
    var chars [26]int
    for i := 0; i < len(s); i++ {
        chars[s[i]-'a']++
        chars[t[i]-'a']--
    }
    for _, c := range chars {
        if c != 0 {
            return false
        }
    }
    return true
}